The invention relates to road restraint system parts, in particular poles for road safety barriers.
Various types of road safety barriers have been developed. One such type comprises horizontally disposed rails mounted on spaced-apart poles let into the ground.
Conventional poles for road safety barriers are normally made of steel, aluminium, wood, concrete, or natural stone. These materials are expensive due to the material costs, their installation, transport, and repairing costs. In addition, wooden poles can form dangerous sharp broken pieces which in the event of a collision may flung around in the area of the accident so that they constitute a danger in themselves. Above that, sharp pieces of wooden poles can penetrate the car body and create an additional risk for passengers. Since wooden poles are impregnated with toxic chemicals to provide better weather resistance and rot protection, they also cause environmental concerns. For instance in Norway an additional fee has to be paid upon of these toxically impregnated poles.
Since it is the purpose of road safety barriers to prevent a vehicle which goes out of control from driving into the roadside ditch, down a slope, over a drop, or into a lane with traffic in the opposite direction, it is important that these barriers are able to withstand the force in order to keep the vehicles on the road. Thus, a high energy absorption of the poles is one of the crucial factors of road safety barriers. However, wooden poles are rigid and poles made of concrete and stone are rigid and brittle. Thus, when the conventional poles break the energy absorption will mainly be taken case of by the vehicle giving also large damages on the vehicle and the driver/passenger. Poles of galvanised steel and zinc may leak out, especially since the poles are in direct contact with the soil. When steel poles are bent to the ground they are not more active in the energy absorbing process due to their plastic behaviour. Plastic poles are acting more as an elastic object which is recovering to its original position when the load is not active, i.e. the same poles are ready for absorbing additional energy, also during the same collision event due to the whole system of poles and guard rails.
To overcome at least some of the drawbacks of conventional poles, the use of plastic poles for road safety barriers has been proposed. For instance, U.S. Pat. No. 5,507,473 discloses a pole for a road safety barrier comprising a metal pipe with lugs embedded into a plastic material consisting of a blend of high-density polyethylene and low-density polyethylene to give the necessary temperature stability. U.S. Pat. No. 5,660,375 discloses a multi-layer pole of polyester veils and fibreglass nets filled with recycled plastic. U.S. Pat. No. 5,152,507 proposes a pole consisting of a rod of fibre-reinforced plastic filled with foamed plastic which is inserted into a pipe of fibre-reinforced plastic embedded into concrete. Compared to conventional poles as of wood, for instance, these poles are much too expensive.
In addition, poles for road safety barriers are known as being one-piece moldings of plastic material such as a mixture of high- or low-density polyethylene or polypropylene (U.S. Pat. No. 5,219,241) or a hollow plastic pipe (WO99/61708). However, these poles bend upon collision with a car. To overcome this problem, WO99/61708 suggests a specific system for fastening the guard rail to the poles which leads the car back to the road when the poles are bent, i.e. WO99/61708 is utilising the bending for energy absorption.
Since it is a well known property of poles made of plastic such as polyethylene to bend easily, poles of plastic are also widely used as traffic guide poles (CH-A-471940, CH-A-546862, DE-C-2649911).
Because of their unsatisfactory energy absorption, the prior art poles made of plastic fail when a vehicle crashes at high speed into the safety barrier, particularly under cold climate-conditions. Under these conditions, plastic becomes brittle and will practically make no contribution to the energy absorption badly needed. In addition, loose parts of the safety barrier as well as remaining sharp pieces of the poles may injure the involved people in such an accident.